This invention is directed to catalysts and related processes useful for sulfur adsorption from sulfur compound containing feedstreams. Specifically, the invention is directed to copper oxide/zinc oxide/aluminum oxide catalyst optionally promoted with an alkali metal, such as K, Rb, Cs, or with a metal selected from the group consisting of Ti, V, Mn, Zr, Mo, Ru, Rh, Pd, Ba, La, Re, Tl, Ce and combinations thereof, useful for sulfur adsorption processes.
As used herein, the term adsorption shall be defined broadly so as to also include absorption, and no attempt shall be made to distinguish adsorption or adsorptive processes from absorption or absorptive processes.
As part of the pretreatment of naphtha feed streams for catalytic reformers and isomerization units, sulfur guards are commonly used to polish the remaining sulfur species that are present after a hydtrotreater. Guard materials often contain either reduced nickel or copper oxide. Nickel adsorbents are very effective at adsorbing most if not all of the sulfur compounds from the feed stream. Copper containing adsorbents are also effective at taking out sulfur, especially H2S, but are known to allow other sulfur compounds to partially or completely pass through the guard bed, including sulfides and thiophenes. Depending on the catalyst and application, the fact that some sulfur passes through a guard bed may be acceptable since sulfur is often used to moderate the downstream catalyst performance to the desired level. In general, however, thiophenes are less desirable as the sulfur form than, for example, disulfides.
In addition to adsorbents, a number of different catalysts are known in the art that are effective for removing sulfur compounds. For example, activated carbon has a high capacity for ethyl mercaptans, manganese oxide is effective for dimethyl sulfoxide removal, and zinc oxide can be used to remove hydrogen sulfide. Other catalysts known to be effective in desulfurization processes include carbon, copper/zinc oxides, nickel-based sorbents, nickel oxides, zeolites, molecular sieves and faujasites, among others. In addition, different methods have been used to reduce the sulfur level in feedstreams, such as prior art hydrodesulfurization (HDS) processes. These processes are usually carried out at high temperatures and pressures, so they are relatively expensive processes. Further, the HDS processes normally only reduce the sulfur content in gasoline feedstreams to levels of about 200 ppm whereas it is desirable to reduce the sulfur content to about 10 ppm. Thus, a better method for removal of unacceptable sulfur-containing compounds is needed.